Ignition coil assemblies typically have an electrically insulating material between the primary coil and the secondary coil. Earlier ignition coil assembly designs used liquid oil as the electrically insulating material. Some more recent ignition coil assembly designs use epoxy resin-based materials as an electrically insulating material due to improved mechanical properties. Since epoxy resin-based materials typically harden, they may offer additional mechanical support to ignition coil components.
One disadvantage of epoxy resin-based materials, where filler content is part of the formulation, is the need for spaces to allow the proper flow of epoxy within coil sub assembles when it is poured or injected into the ignition coil assembly. The lack of spaces to allow the proper flow of epoxy may create voids in the material after it hardens. These voids may not offer enough dielectric strength to insulate a high voltage in the secondary coil from a lower voltage in the primary coil. This may cause arcing between the primary coil and the secondary coil that may result in a lower secondary voltage output and poor energy delivery from the ignition coil assembly. Arcing may also damage the ignition coil assembly. Therefore, it is preferable to avoid the formation of voids in the electrically insulating material between the primary coil and the secondary coil.